Symmetry analysis of complex magnetic structure in monoclinically distorted Er3Cu4Sn4.

The magnetic structure in Er3Cu4Sn4 has been determined using high-resolution powder neutron diffraction, supported by symmetry analysis. At low temperatures, Er3Cu4Sn4 assumes a crystal structure of the Tm3Cu4Sn4 type (in the monoclinic space group C2/m). The Er atoms occupy two distinct Wyckoff sites: 2c and 4i. It has been found that the Er magnetic moments on the 2c site form a commensurate antiferromagnetic structure (k1 = [0, 0, ½]) below 6 K. The magnetic moments reach 8.91 (8) μB at 1.4 K and are parallel to the b axis. The Er magnetic moments on the 4i site order below 2 K and form an incommensurate antiferromagnetic sine-modulated structure (k2 = [1, 0.4667 (1), ½]), with magnetic moments lying in the ac plane and perpendicular to the a axis. The amplitude of modulation equals 8.7 (1) μB at 1.4 K.